Modification of membrane fatty acid composition, eicosanoid production, and phospholipase A activity in Atlantic salmon (Salmo salar) gill and kidney by dietary lipid

Impact of dietary level and ratio of n-6 and n-3 fatty acids on disease progression and mRNA expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) challenged with Paramoeba perurans

The aim of the study was to investigate the influence of dietary level and ratio of n-6/n-3 fatty acids (FA) on growth, disease progression and expression of immune and inflammatory markers in Atlantic salmon (Salmo salar) following challenge with Paramoeba perurans. Fish (80 g) were fed four different diets with different ratios of n-6/n-3 FA; at 1.3, 2.4 and 6.0 and one diet with ratio of 1.3 combined with a higher level of n-3 FA and n-6 FA. The diet with the n-6/n-3 FA ratio of 6.0 was included to ensure potential n-6 FA effects were revealed, while the three other diets were more commercially relevant n-6/n-3 FA ratios and levels. After a pre-feeding period of 3 months, fish from each diet regime were challenged with a standardized laboratory challenge using a clonal culture of P. perurans at the concentration of 1,000 cells L⁻¹. The subsequent development of the disease was monitored (by gross gill score), and sampling conducted before challenge and at weekly sampling points for 5 weeks post-challenge. Challenge with P. perurans did not have a significant impact on the growth of the fish during the challenge period, but fish given the feed with the highest n-6/n-3 FA ratio had reduced growth compared to the other groups. Total gill score for all surfaces showed a significant increase with time, reaching a maximum at 21 days post-challenge and declined thereafter, irrespective of diet groups. Challenge with P. perurans influenced the mRNA expression of examined genes involved in immune and inflammatory response (TNF-α, iNOS, IL4-13b, GATA-3, IL-1β, p53, COX2 and PGE₂-EP4), but diet did not influence the gene expression. In conclusion, an increase in dietary n-6/n-3 FA ratio influenced the growth of Atlantic salmon challenged with P. perurans; however, it did not alter the mRNA expression of immune genes or progression of the disease.

Shotgun Lipidomics for the Determination of Phospholipid and Eicosanoid Profiles in Atlantic Salmon (Salmo salar L.) Muscle Tissue Using Electrospray Ionization (ESI)-MS/MS Spectrometric Analysis

Shotgun lipidomics was applied to identify and quantify phospholipids (PLs) in salmon muscle tissue by focusing on the distribution of ω-3 fatty acids (e.g., docosahexaenoic acid (DHA) and eicosapentaenoic acid (EPA)) in the form of phospholipids, as well as to identify and quantify eicosanoids, which has not yet been attempted in Atlantic salmon muscle. Shotgun lipidomics enabled the identification of 43 PL species belonging to four different classes: phosphatidylcholines (PCs), phosphatidylethanolamines (PEs), phosphatidylserines (PSs), and phosphatidylinositols (PIs). Among others, 16:0-22:6 PtdCho m/z [M + Na]⁺ at 828.4 was the predominant PL species in salmon muscle tissue. The present study provided the quantification of individual phospholipid species, which has not been performed for salmon muscle tissue so far. In addition, two eicosanoids-prostaglandin E2 (PGE2) and prostaglandin F3α (PGF3α)-were identified for the first time in salmon muscle. Thus, the rapid and high-throughput shotgun lipidomics approach should shed new light on phospholipids and eicosanoids in salmon muscle tissue.

Effect of replacement of dietary fish oil with four vegetable oils on prostaglandin E2 synthetic pathway and expression of inflammatory genes in marine fish Larimichthys crocea

As a lipid mediator with important immune function, prostaglandin E₂ (PGE₂) has been widely studied in mammals, whereas its synthetic pathway and immune function in fish have yet to be fully studied. To investigate the regulation of PGE₂ synthetic pathway and inflammatory genes expression by dietary different oils and the underlying relationship, a 10-week feeding experiment and an immune challenge were carried out in marine fish Larimichthys crocea. Replacement of dietary fish oil (FO) with four vegetable oils (VO), including soybean oil, linseed oil, palm oil, and olive oil, all reduced PGE₂ levels, and the decrease of arachidonic acid (ARA, substrate for PGE₂) could account for this decline. Meanwhile, the expression of PGE₂ synthesis related genes was basically upregulated, which seemed to be a feedback regulation, but it cannot compensate the deficiency of ARA. In addition, mRNA expression of inflammatory genes, including interleukin (IL)-1β, IL-6, tumor necrosis factor (TNF)α and interferon (IFN)γ was all upregulated in four VO groups compared with FO group, which was the opposite of PGE₂ levels. To verify the inflammatory regulation of PGE₂, an immune challenge was conducted, and PGE₂ alleviated LPS-induced expression of inflammatory genes, including IL-6, TNFα and IFNγ, and the similar downregulation of toll-like receptor (TLR) genes expression revealed that TLR signaling pathway participated in the anti-inflammatory regulation of PGE₂. In conclusion, replacement of dietary FO with four VO (lack of ARA) reduced the levels of PGE₂ that could alleviate LPS-induced inflammatory genes expression via TLR signaling pathway, which could be one of the reasons that VO induced inflammation in marine fish.

Alternatively spliced variants in Atlantic cod (Gadus morhua) support response to variable salinity environment

Analysis of gill transcriptome of the Atlantic cod from the Baltic Sea demonstrated that alternatively spliced (AS) variants may be actively involved in the process of adaptation to altered salinity. Some AS variants of different genes, like phospholipase A2 group IVC (PLA2G4C), appeared only in fish exposed to altered salinity, while other isoforms of the same genes were present in all experimental groups. Novel sequence arrangements represent 89% of all AS in the Baltic cod compared to the Atlantic population. Profiles of modified pathways suggest that regulation by AS can afford specific changes of genes expressed in response to the environment. The AS variants appear to be involved in the response to stress by modifications of signalling in apoptosis pathways, an innate immunological response and pro-inflammatory process. Present results support the hypothesis that developing new AS variants could support genome complexity and reinforce the ability to fast adapt to local environments.

Effects of dietary n-3 fatty acids on Toll-like receptor activation in primary leucocytes from Atlantic salmon (Salmo salar)

The shortage of the n-3 fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) on the international markets has led to increasing substitution of fish oil by plant oils in Atlantic salmon (Salmo salar) feed and thereby reducing the EPA and DHA content in salmon. However, the minimum required levels of these fatty acids in fish diets for securing fish health are unknown. Fish were fed with 0, 1 or 2% EPA or DHA alone or in combination of both over a period, growing from 50 to 400 g. Primary head kidney leucocytes were isolated and stimulated with Toll-like receptor (TLR) ligands to determine if EPA and DHA deficiency can affect expression of important immune genes and eicosanoid production. Several genes related to viral immune response did not vary between groups. However, there was a tendency that the high-level EPA and DHA groups expressed lower levels of IL-1β in non-stimulated leucocytes. These leucocytes were also more responsive to the TLR ligands, inducing higher expression levels of IL-1β and Mx1 after stimulation. The levels of prostaglandin E2 and leukotriene B4 in serum and media from stimulated leucocytes were lower in both low and high EPA and DHA groups. In conclusion, leucocytes from low EPA and DHA groups seemed to be less responsive towards immunostimulants, like TLR ligands, indicating that low levels or absence of dietary EPA and DHA may have immunosuppressive effects.

Dietary Mannan Oligosaccharides: Counteracting the Side Effects of Soybean Meal Oil Inclusion on European Sea Bass (Dicentrarchus labrax) Gut Health and Skin Mucosa Mucus Production?

The main objective of this study was to assess the effects of 4 g kg(-1) dietary mannan oligosaccharides (MOS) inclusion in soybean oil (SBO)- and fish oil (FO)-based diets on the gut health and skin mucosa mucus production of European sea bass juveniles after 8 weeks of feeding. Dietary MOS, regardless of the oil source, promoted growth. The intestinal somatic index was not affected, however dietary SBO reduced the intestinal fold length, while dietary MOS increased it. The dietary oil source fed produced changes on the posterior intestine fatty acid profiles irrespective of MOS dietary supplementation. SBO down-regulated the gene expression of TCRβ, COX2, IL-1β, TNFα, IL-8, IL-6, IL-10, TGFβ, and Ig and up-regulated MHCII. MOS supplementation up-regulated the expression of MHCI, CD4, COX2, TNFα, and Ig when included in FO-based diets. However, there was a minor up-regulating effect on these genes when MOS was supplemented in the SBO-based diet. Both dietary oil sources and MOS affected mean mucous cell areas within the posterior gut, however the addition of MOS to a SBO diet increased the mucous cell size over the values shown in FO fed fish. Dietary SBO also trends to reduce mucous cell density in the anterior gut relative to FO, suggesting a lower overall mucosal secretion. There are no effects of dietary oil or MOS in the skin mucosal patterns. Complete replacement of FO by SBO, modified the gut fatty acid profile, altered posterior gut-associated immune system (GALT)-related gene expression and gut mucous cells patterns, induced shorter intestinal folds and tended to reduce European sea bass growth. However, when combined with MOS, the harmful effects of SBO appear to be partially balanced by moderating the down-regulation of certain GALT-related genes involved in the functioning of gut mucous barrier and increasing posterior gut mucous cell diffusion rates, thus helping to preserve immune homeostasis. This denotes the importance of a balanced dietary n-3/n-6 ratio for an appropriate GALT-immune response against MOS in European sea bass juveniles.

Effects of functional feeds on the lipid composition, transcriptomic responses and pathology in heart of Atlantic salmon (Salmo salar L.) before and after experimental challenge with Piscine Myocarditis Virus (PMCV)

Background

Cardiomyopathy syndrome (CMS) is a severe cardiac disease of Atlantic salmon (Salmo salar) recently associated with a double-stranded RNA virus, Piscine Myocarditis Virus (PMCV). The disease has been diagnosed in 75-85 farms in Norway each year over the last decade resulting in annual economic losses estimated at up to €9 million. Recently, we demonstrated that functional feeds led to a milder inflammatory response and reduced severity of heart lesions in salmon experimentally infected with Atlantic salmon reovirus, the causal agent of heart and skeletal muscle inflammation (HSMI). In the present study we employed a similar strategy to investigate the effects of functional feeds, with reduced lipid content and increased eicosapentaenoic acid levels, in controlling CMS in salmon after experimental infection with PMCV.

Results

Hepatic steatosis associated with CMS was significantly reduced over the time course of the infection in fish fed the functional feeds. Significant differences in immune and inflammatory responses and pathology in heart tissue were found in fish fed the different dietary treatments over the course of the infection. Specifically, fish fed the functional feeds showed a milder and delayed inflammatory response and, consequently, less severity of heart lesions at earlier and later stages after infection with PMCV. Decreasing levels of phosphatidylinositol in cell membranes combined with the increased expression of genes related with T-cell signalling pathways revealed new interactions between dietary lipid composition and the immune response in fish during viral infection. Dietary histidine supplementation did not significantly affect immune responses or levels of heart lesions.

Conclusions

Combined with the previous findings on HSMI, the results of the present study highlight the potential role of clinical nutrition in controlling inflammatory diseases in Atlantic salmon. In particular, dietary lipid content and fatty acid composition may have important immune-modulatory effects in Atlantic salmon that could be potentially beneficial in fish balancing the immune and tissue responses to viral infections.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-462) contains supplementary material, which is available to authorized users.

Influence of dietary docosahexaenoic acid in combination with other long-chain polyunsaturated fatty acids on expression of biosynthesis genes and phospholipid fatty acid compositions in tissues of post-smolt Atlantic salmon (Salmo salar)

To investigate interactions of dietary LC-PUFA, a dose-response study with a range of docosahexaenoic acid (DHA; 22:6n-3) levels (1 g kg(-1), 5 g kg(-1), 10 g kg(-1), 15 g kg(-1) and 20 g kg(-1)) was performed with post-smolts (111 ± 2.6g; mean ± S.D.) over a nine-week feeding period. Additional diets included 10 g kg(-1) DHA in combination with 10 g kg(-1) of either eicosapentaenoic acid (EPA; 20:5n-3) or arachidonic acid (ARA; 20:4n-6), and a diet containing 5 g kg(-1) each of DHA and EPA. The liver, brain, head kidney and gill were collected at the conclusion of the trial, and lipid and fatty acid compositions were determined as well as expression of genes of LC-PUFA biosynthesis. Total lipid content and class composition were largely unaffected by changes in dietary LC-PUFA. However, phospholipid (PL) fatty acid compositions generally reflected that of the diet, although the response varied between tissues. The liver most strongly reflected diet, followed by the head kidney. In both tissues increasing dietary DHA led to significantly increased DHA in PL and inclusion of EPA or ARA led to higher levels of these fatty acids. The brain showed the most conserved composition and gene expression profile, with increased dietary LC-PUFA resulting in only minor changes in PL fatty acids. Dietary LC-PUFA significantly affected the expression of Δ6 and Δ5 desaturases, Elovl 2, 4 and 5, and SREBPs although this varied between tissues with greatest effects observed in the liver followed by the head kidney, similar to PL fatty acid compositions.

Effects of thermal acclimation on tissue fatty acid composition of freshwater alewives (Alosa pseudoharengus)

In this study, we examine changes in fatty acid composition of polar and neutral lipids in gill, liver, and muscle of freshwater alewives (Alosa pseudoharengus) after temperature challenges in the laboratory. Alewives experienced either a warm or cold challenge in which temperatures were raised or lowered 0.5°C day(-1) over 4-6 weeks. In alewives experiencing the cold challenge, gill polar lipids showed evidence of significant remodeling, including decreases in palmitic acid and saturated fatty acids and increases in n-3 and n-6 highly unsaturated fatty acids including docosahexaenoic acid (DHA) and arachidonic acid. In alewives experiencing the warm challenge, we observed significant increases in saturated fatty acids (due mainly to increased palmitic acid) and decreases in polyunsaturated fatty acids in polar lipids of muscle and liver tissue. Fish that died during the cold challenge had significantly higher levels of palmitic acid in muscle polar lipids compared to fish that survived; fish that died during the warm challenge displayed complex changes in fatty acid composition. Based on theoretical considerations, the changes in polar lipids we observed during thermal acclimation are likely to promote appropriate membrane fluidity under each thermal regime. The increased incorporation of highly unsaturated fatty acids during cold acclimation could have significant physiological and ecological implications. In particular, since highly unsaturated fatty acids are typically scarce in freshwater food webs, dietary deficiencies in these essential fatty acids may be a significant factor in winter mortality of freshwater alewives.

Effects of a diet lacking HUFA on lipid and fatty acid content of intestine and gills of male gilthead seabream (Sparus aurata L.) broodstock at different stages of the reproductive cycle

A feeding experiment was carried out to determine the effect of a diet lacking n-3 and n-6 highly unsaturated fatty acids (HUFA) on lipid and fatty acid content in intestine and gills of male gilthead seabream (Sparus aurata L.) broodstock at different stages of the reproductive cycle: November (pre-spermatogenesis), March (spermatogenesis), and June (post-spermatogenesis). For this purpose, gilthead seabream broodstock were fed either a control diet (C) or an n-3 and n-6 HUFA-deficient diet (D). The results showed no changes in fatty acid content of polar lipids of intestine and gills from fish fed diet C at different stages of the reproductive cycle. However, significant changes were observed in the fatty acid content of neutral lipids in intestine but not in gills in this group. Thus, between November and March, saturates and n-3 HUFA decreased while monoenes increased. In June, the contents of these fatty acids had returned to their initial values (November). Moreover, in fish fed diet D, the fatty acid content of neutral lipid changed in both intestine and gills. In intestine NL, a decrease in saturates and n-3 HUFA and an increment in monoenes were observed from November to June. In gills, a decrease was also observed in n-3 HUFA from NL along the cycle. Nevertheless, n-6 HUFA content remained unchanged. These results show both tissue specificity in seasonal mobilization of fatty acids linked to reproductive processes and the influence of dietary fatty acids on body composition.

Dietary fatty acids and inflammation in the vertebral column of Atlantic salmon, Salmo salar L., smolts: a possible link to spinal deformities

Vegetable oils (Vo) are an alternative to fish oil (Fo) in aquaculture feeds. This study aimed to evaluate the effect of dietary soybean oil (Vo diet), rich in linoleic acid, and of dietary fish oil (Fo diet) on the development of spinal deformities under bacterial lipopolysaccharide (LPS)-induced chronic inflammation conditions in Atlantic salmon, Salmo salar L. Fish [25 g body weight (BW)] were fed the experimental diets for 99 days. On day 47 of feeding (40 g BW), fish were subjected to four experimental regimes: (i) intramuscular injections with LPS, (ii) sham-injected phosphate-buffered saline (PBS), (iii) intraperitoneally injected commercial oil adjuvant vaccine, or (iv) no treatment. The fish continued under a common feeding regime in sea water for 165 more days. Body weight was temporarily higher in the Vo group than in the Fo group prior to immunization and was also affected by the type of immunization. At the end of the trial, no differences were seen between the dietary groups. The overall prevalence of spinal deformities was approximately 14% at the end of the experiment. The Vo diet affected vertebral shape but did not induce spinal deformities. In groups injected with LPS and PBS, spinal deformities ranged between 21% and 38%, diet independent. Deformed vertebrae were located at or in proximity to the injection point. Assessment of inflammatory markers revealed high levels of plasma prostaglandin E₂ (PGE₂) in the Vo-fed and LPS-injected groups, suggesting an inflammatory response to LPS. Cyclooxigenase 2 (COX-2) mRNA expression in bone was higher in fish fed Fo compared to Vo-fed fish. Gene expression of immunoglobulin M (IgM) was up-regulated in bone of all LPS-injected groups irrespective of dietary oil. In conclusion, the study suggests that Vo is not a risk factor for the development of inflammation-related spinal deformities. At the same time, we found evidence that localized injection-related processes could trigger the development of vertebral body malformations.

Effects of partial substitution of dietary fish oil with blends of vegetable oils, on blood leucocyte fatty acid compositions, immune function and histology in European sea bass (Dicentrarchus labrax L.)

Within a decade or so insufficient fish oil (FO) will be available to meet the requirements for aquaculture growth. Consequently, alternative sources are being investigated to reduce reliance on wild fish as a source of FO. Vegetable oils (VO) are a feasible alternative to FO. However, it is important to establish that alternative dietary lipids are not only supplied in the correct quantities and balance for optimal growth, but can maintain immune function and prevent infection, since it is known that the nutritional state of the fish can influence their immune function and disease resistance. A way of maintaining immune function, while replacing dietary FO, is by using a blend of VO rather than a single oil. In this study, juvenile European sea bass (Dicentrarchus labrax) were fed diets with a 60 % substitution of FO with a blend of rapeseed, linseed and palm oils. Two oil blends were used to achieve a fatty acid composition similar to FO, in terms of energy content, and provide a similar balance of SFA, MUFA and PUFA. Fish were fed the diets for 64 weeks, after which time growth and fatty acid compositions of liver and blood leucocytes were monitored. The impact of the dietary blends on selected innate immune responses and histopathology were also assessed, together with levels of plasma prostaglandin E2. The results suggest that potential exists for replacing FO with a VO blend in farmed sea bass feeds without compromising growth, non-specific immune function or histology.

Pre- and post-challenge immuno-haematological changes in Labeo rohita juveniles fed gelatinised or non-gelatinised carbohydrate with n-3 PUFA

The combined effect of dietary carbohydrate type and n-3 PUFA (EPA+DHA) on pre- and post-challenge haemato-immunological responses in Labeo rohita juveniles was studied. Fish were fed for 67days with six different test diets containing either gelatinised (G) or non-gelatinised (NG) corn (43%) with three levels of n-3 PUFA (0.5%, 1.0% and 2.0%). During the pre-challenge period, significantly higher (P<0.05) NBT, serum lysozyme activity, total protein and globulin content was recorded in the NG carbohydrate fed groups. Highest NBT value was recorded in the groups fed with 1.0% n-3 PUFA, whereas the highest serum lysozyme activity (P<0.05) was recorded at either 0.5% or 2.0% n-3 PUFA fed groups in both the pre- and post-challenge period. Feeding of NG corn significantly increased the total leucocyte count, lysozyme activity, A/G ratio and decreased the total erythrocyte count, haemoglobin, serum total protein and globulin content of L. rohita juveniles during the post-challenge period. Similarly, feeding of n-3 PUFA at any level significantly increased the immunological parameters like lysozyme activity or A/G ratio, whereas total leukocyte count increased due to feeding of either 0.5% or 1.0% n-3 PUFA. The NBT and albumin values remained similar in both the pre- and post-challenge period. After challenge with Aeromonas hydrophila, the highest survival was recorded in the NG carbohydrate fed groups, whereas the lowest survival was recorded in the highest level of n-3 PUFA fed group irrespective of dietary carbohydrate type. Thus, a high level of G carbohydrate as well as n-3 PUFA is found to be immunosuppressive in L. rohita juveniles. NG carbohydrate supplemented with 1.0% n-3 PUFA is found to be optimum to enhance the immunity in L. rohita juveniles.

Divergent cyclooxygenase responses to fatty acid structure and peroxide level in fish and mammalian prostaglandin H synthases

Prostanoid synthesis in mammalian tissues is regulated at the level of prostaglandin H synthase (PGHS) cyclooxygenase catalysis by the availability and structure of substrate fatty acid and the availability of peroxide activator. Two major PGHS isoforms, with distinct pathophysiological functions and catalytic regulation, have been characterized in mammals; a functionally homologous PGHS isoform pair has been cloned from an evolutionarily distant vertebrate, brook trout. The cyclooxygenase activities of recombinant brook trout PGHS-1 and -2 were characterized to test the generality of mammalian regulatory paradigms for substrate specificity, peroxide activation, and product shifting by aspirin. Both trout cyclooxygenases had much more restrictive substrate specificities than their mammalian counterparts, with pronounced discrimination toward arachidonate (20:4n-6) and against eicosapentaenoate (20:5n-3) and docosahexaenoate (22:6n-3), the latter two prominent in trout tissue lipids. Aspirin treatment did not increase lipoxygenase-type catalysis by either trout enzyme. Both trout enzymes had higher requirements for peroxide activator than their mammalian counterparts, though the preferential peroxide activation of PGHS-2 over PGHS-1 seen in mammals was conserved in the fish enzymes. The divergence in cyclooxygenase characteristics between the trout and mammalian PGHS proteins may reflect accomodations to differences among vertebrates in tissue lipid composition and general redox state.

Effect of dietary lipids on plasma fatty acid profiles and prostaglandin and leptin production in gilthead seabream (Sparus aurata)

The aim of this study was to investigate the effects of different levels of substitution of fish oil by vegetable oils rich in oleic, linoleic and linolenic acids on gilthead seabream plasma and leukocyte fatty acid compositions and prostaglandin (PG) and leptin production. Juvenile seabream of 24 g initial body mass were fed four iso-energetic and iso-proteic experimental diets for 281 days. Fatty acid composition of plasma lipids was markedly affected by the inclusion of vegetable oils (VO). ARA (arachidonate), EPA (eicosapentaenoate) and DHA (docosahexaenoate) were preferentially incorporated into polar lipids of plasma, and DHGLA (di-homogammalinoleate) accumulated with increased vegetable oil inclusion. Dietary treatments resulted in alterations of DHGLA/ARA ratios, but not ARA/EPA. ARA-derived PGE(2) production in plasma was not affected by vegetable oils, in agreement with similar eicosanoid precursor ratio (ARA/EPA) in leukocytes total lipids and plasma phospholipids among fish fed with the different dietary treatments. Feeding vegetable oils leads to a decrease in plasma EPA which in turn reduced plasma PGE(3) concentration. Moreover, PGE(3) was the major prostaglandin produced in plasma of fish fed fish oil based diet. Such findings point out the importance of EPA as a precursor of prostaglandins in marine fish, at least for the correct function of the blood cells, and correlates well with the predominant role of this fatty acid in immune regulation in this species. A negative correlation was found between plasma PGE(2) and leptin plasma concentration, suggesting that circulating levels of leptin may act as a metabolic signal modulating PGE(2) release. The present study has shown that increased inclusion of vegetable oils in diet for gilthead seabream may profoundly affect the fatty acid composition of plasma and leukocytes, specially HUFA (highly unsaturated fatty acids), and consequently the production of PGE(3), which can be a major PG in plasma. Alteration in the amount and type of PG produced can be at least partially responsible for the changes in the immune system and health parameters of fish fed diets with high inclusion of VO.

Polyunsaturated fatty acid profiles of whole body phospholipids and triacylglycerols in anadromous and landlocked Atlantic salmon (Salmo salar L.) fry

We compared the fatty acid compositions and gains of whole body triacylglycerols (TAG) and phospholipids (PL) in anadromous and landlocked Atlantic salmon (Salmo salar) fry, of the same age, fed the same commercial marine oil-rich diet over a 42-day feeding trial. The landlocked strain exhibited significantly (P<0.05) higher growth rate and feed efficiency, due principally to a higher fat retention, particularly of monounsaturated and saturated fatty acids (SFA). n-3 and n-6 long-chain polyunsaturated fatty acid (PUFA) gains and retentions were significantly higher (P<0.05) in the landlocked fry. Great similarities were found in the fatty acid profiles of whole body TAG of both strains. However, marked genotypic differences were observed in the PUFA profiles of whole body PL fractions. The total PUFA, n-3 PUFA and docosahexaenoic acid (DHA) level in PL was significantly higher (P<0.05) while the SFA level, and the PUFA C18/C20 and eicosapentaenoic acid/arachidonic acid ratios were significantly lower (P<0.05) in the anadromous fry than in landlocked fry. Our results indicate that the level of DHA in salmon PL is under strong genetic control and that the capacity for incorporation, and possibly for the conversion of dietary n-3 and n-6 PUFA, is higher in the landlocked strain.

The effects of dietary lipid and strain difference on polyunsaturated fatty acid composition and conversion in anadromous and landlocked salmon (Salmo salar L.) parr

Five experimental diets containing different proportions of olive, sunflower and linseed oils were used in a 55-day feeding trial on both anadromous and landlocked parr of Atlantic salmon (Salmo salar) of the same age, in order to study the effects of diet and strain on growth and fatty acid composition and absolute gains in fish whole body triacylglycerols (TAG) and phospholipids (PL). Growth rate was higher in landlocked than in anadromous parr, but not between the different diets. By contrast, the effect of diet on whole body fatty acid composition was much more pronounced than that of strain difference. The fatty acids deposition results establish significant (P<0.05) positive correlations and linear relationships between the percentage of several fatty acids (18:1n-9, 18:2n-6, 18:3n-3) in dietary lipids and their absolute gains in whole body TAG and PL of both stocks. They also indicate the selective deposition of 18:1n-9 compared with linoleic acid (LLA) and linolenic acid (LNA). Finally, the results suggest the occurrence of the conversion of LLA and LNA to long-chain polyunsaturated fatty acids, its stimulation by increased substrate availability, a significantly higher n-3 and n-6 polyunsaturated fatty acids conversion capacity in landlocked than in anadromous parr and a strong genetic influence on docosahexaenoic acid content in salmon parr PL.

Modulation of arachidonate and docosahexaenoate in Morone chrysops larval tissues and the effect on growth and survival

The extent to which extreme dietary levels of arachidonate (AA) and/or docosahexaenoate (DHA) modulate lipid composition in the body tissues and consequently affect growth and survival in freshwater Morone larvae species was examined. White bass, M. chrysops, larvae (day 24-46) were fed Artemia nauplii enriched with algal oils containing varying proportions of AA and DHA (from 0 to over 20% the total fatty acids). Growth was significantly reduced (P< 0.05) in larvae fed a DHA-deficient Artemia diet. Increases in dietary levels of AA also were associated with a significant growth reduction. However, the inhibitory effect of AA on larvae growth could be suppressed by the dietary addition of DHA (at a level of 21.6% of the total fatty acids in enrichment lipids). Larval brain + eyes tissue accumulated over 10 times more DHA than AA in its structural lipids (phosphatidylcholine, phosphatidylethanolamine) at any dietary ratio. In contrast, DHA accumulation, as compared to AA, in gill lipids declined considerably at higher than 10:1 DHA/AA tissue ratios. DHA and eicosapentaenoic acid (EPA) contents in brain + eyes tissue were most sensitive to competition from dietary AA, being displaced from the tissue at rates of 0.36 +/- 0.07 mg DHA and 0.46 +/- 0.11 mg EPA per mg increase in tissue AA, and 0.55 +/- 0.14 mg AA per mg increase in tissue DHA. On the other hand, AA and EPA levels in gill tissue were most sensitive to dietary changes in DHA levels; AA was displaced at rates of 0.37 +/- 0.11 mg, whereas EPA increased at rates of 0.68 +/- 0.28 mg per mg increase in tissue DHA. Results suggest that balanced dietary DHA/AA ratios (that allow DHA/AA ratios of 2.5:1 in brain + eyes tissue) promote a high larval growth rate, which also correlates with maximal regulatory response in tissue essential fatty acids.

Effect of soybean oil and fish oil on individual molecular species of Atlantic salmon head kidney phospholipids determined by normal-phase liquid chromatography coupled to negative ion electrospray tandem mass spectrometry

The effect of soybean oil (SO) and fish oil (FO) on the relative molecular species distribution of phosphatidylcholine (PC), phosphatidylethanolamine (PE), phosphatidylinositol (PI) and phosphatidylserine (PS) in Atlantic salmon head kidney was studied using normal-phase liquid chromatography coupled with negative ion electrospray tandem mass spectrometry. The conformation of identity of the phospholipid species was based on retention time, the mass of the [M-H]- ([M-15]- for PC) molecular ions and the carboxylate anion fragments in the product ion spectrum. The intensity ratio of sn-1/sn-2 fragment ions increased with increasing number of double bonds in the sn-2 acyl chain but was not affected by increasing number of double bonds in the sn-1 acyl chain of the species examined. The relative distribution of the molecular species was determined by multiple reaction monitoring of the carboxylate anion fragment from the sn-1 position. A total of 68 different phospholipid species were determined in the head kidney and the largest amount was found in PE (22 species). Depending on the diet, the main species identified in the different phospholipid classes were; PC 16:0/18:1, PE 16:0/22:6, PI 18:0/20:4 and PS 16:0/22:6. The SO diet significantly increased the 18:2, 20:3 and most 20:4 containing species and significantly reduced the 14:0 and most 20:5 and 22:6 fatty acid containing species. The increase of the 20:4 and the decrease of the 20:5 and 22:6 containing species were dependent on the fatty acid combination of the species.

Dietary n-3 long-chain polyunsaturated fatty acid deprivation, tissue lipid composition, ex vivo prostaglandin production, and stress tolerance in juvenile Dover sole (Solea solea L.)

Larval Dover sole fed an Artemia diet supplemented with n-3 long-chain (C20 + C22) polyunsaturated fatty acids (PUFA) are known to be more resistant to low-temperature injury. Here we explore the relationship between tissue fatty acid composition and tolerance of stressful environmental conditions over the larval and early juvenile periods. Artemia nauplii supplemented with n-3 long-chain PUFA-deficient and PUFA-enriched oil emulsions were fed to two groups of larvae. Whole body tissue samples from the resulting PUFA-deficient and -enriched juveniles possessed 12.1 and 21.9% n-3 long-chain PUFA, respectively. These differences were at the expense of C18 PUFA, while proportions of saturated fatty acids, monounsaturated fatty acids, and total PUFA were unaffected. Brain and eye tissues from the PUFA-deficient fish contained lower levels of 22:6n-3, known to be important for optimal nervous system function, incorporating instead a range of fatty acids of lower unsaturation. PUFA-deprived juveniles showed substantially greater mortality when exposed to a combination of low temperature and low salinity, as well as to high temperature and to hypoxia. After adaptation to the different diets, both dietary groups were fed a common formulated feed high in n-3 long-chain PUFA. Tissue PUFA in both groups progressively increased to the same high value, with a consequent loss of the differences in cold-susceptibility. These correlated changes support a link between dietary manipulation of n-3 long-chain PUFA and development of a stress-sensitive phenotype. PUFA deprivation had no detectable effect upon static hydrocarbon order of purified brain membranes (as assessed by fluorescence polarization) but was associated with an increase in the whole-body content of prostaglandins. We conclude that susceptibility to environmental stress is responsive to dietary n-3 long-chain PUFA manipulation, possibly due to altered tissue development or the overproduction of eicosanoids.

Fatty acyl desaturation in isolated hepatocytes from Atlantic salmon (Salmo salar): stimulation by dietary borage oil containing gamma-linolenic acid

The effects of different dietary oils on the fatty acid compositions of liver phospholipids and the desaturation and elongation or [1-14C]18:3n-3 and [1-14C]18:2n-6 were investigated in isolated hepatocytes from Atlantic salmon. Atlantic salmon smolts were fed diets containing either a standard fish oil (FO) as a control diet, a 1:1 blend of Southern Hemisphere marine oil and tuna orbital oil (MO/TO), sunflower oil (SO), borage oil (BO), or olive oil (OO) for 12 wk. The SO and BO diets significantly increased the percentages of 18:2n-6, 18:3n-6, 20:2n-6, 20:3n-6, and total n-6 polyunsaturated fatty acids (PUFA) in salmon liver lipids in comparison with the FO diet. The BO diet also increased the percentage of 20:4n-6. Both the SO and BO diets significantly reduced the percentages of all n-3 PUFA in comparison with the FO diet. The OO diet significantly increased the percentages of 18:1n-3, 18:2n-6, total monoenes, and total n-6 PUFA in liver lipids compared to the FO diet, and the percentages of all n-3 PUFA were significantly reduced. With [1-14C]18:3n-3, the recovery of radioactivity in the products of delta 6 desaturation was significantly greater in the hepatocytes from salmon fed SO, BO, and OO in comparison with the FO diet. The BO diet also increased the recovery of radioactivity in the products of delta 5 desaturation. Only the BO diet significantly affected the desaturation of [1-14C]18:2n-6, increasing recovery of radioactivity in both delta 6- and delta 5-desaturation products. In conclusion, dietary BO, enriched in gamma-linolenic acid (18:3n-6), significantly increased the proportions of both 20:3n-6 and 20:4n-6 in salmon liver phospholipids and also significantly increased the desaturation of both 18:2n-6 and 18:3n-3 in salmon hepatocytes. The possible relationships between dietary fatty acid composition, tissue phospholipid fatty acid composition, and desaturation/elongation activities are discussed.

Effects of dietary gamma-linolenic acid-rich borage oil combined with marine fish oils on tissue phospholipid fatty acid composition and production of prostaglandins E and F of the 1-, 2- and 3-series in a marine fish deficient in delta5 fatty acyl desaturase

The effects of gamma-linolenic acid-rich borage oil (BO), in combination with different marine oils, namely an eicosapentaenoic acid (EPA) rich oil (MO) or a DHA-rich oil (TO), on tissue fatty acid composition and prostaglandin production were investigated in turbot, a species which lacks appreciable delta5 fatty acyl desaturase activity. The juvenile turbot grew well on the experimental diets and there were no significant differences in final weights between dietary treatments. Irrespective of the marine oil component, both the BO-containing diets increased tissue phospholipid levels of 18:2n-6 and 18:3n-6, and their respective elongation products, 20:2n-6 and 20:3n-6, compared to fish fed a control diet containing a standard Northern hemisphere fish oil. Both the BO-containing diets increased the production of 1-series prostaglandins (PG), this being observed across all tissues investigated with PGF and especially PGE. The BO/MO diet also reduced 20:4n-6 in tissue phospholipids without affecting 20:5n-3, whereas the BO/TO combination decreased 20:5n-3 but increased 20:4n-6. The production of 2-series and 3-series PGs was also altered by the dietary treatments but the changes were less dependent upon the tissue levels of their respective precursor fatty acids, 20:4n-6 and 20:5n-3. The BO-containing diets had very significant effects on gross fatty acid compositions of the phospholipids including increased proportions of saturated fatty acids and n-6 polyunsaturated fatty acids (PUFA) and decreased proportions of monounsaturated fatty acids and n-3 PUFA. Overall, this study shows that eicosanoid production in turbot tissues can be influenced by dietary fatty acids, not only by changes in the absolute and relative levels of specific eicosanoid precursor PUFA in tissue phospholipids, but also by general effects on membrane composition, structure and function induced by gross fatty acid compositional changes.